1. Field of the Invention
The present invention relates to a technology for detecting a motion vector and creating an interpolation frame based on the motion vector.
2. Description of the Related Art
In general, there are two types of display devices, namely, an impulse-type display device and a hold-type display device. The impulse-type display device emits light only for a certain persistence period of fluorescent material after writing an image onto a screen of the display device. A cathode ray tube (CRT) display and a field emission display (FED) are categorized as the impulse-type display device, for example. The hold-type display device holds display of a last image frame until a new image frame is written. A liquid crystal display (LCD) and an electro-luminescence display (ELD) are categorized as the hold-type display device, for example.
One of drawbacks of the hold-type display device is a blur phenomenon that occurs while displaying a moving image. The blur phenomenon occurs because images of a plurality of frames are superposed and reflected in eyes when a moving object appears in the images across the frames and the eyes of an observer follow the movement of the moving object.
Until the previous frame is replaced with the next frame in the displayed image, the same previous frame is kept being displayed. Despite this, the eyes predict display of the next frame of the image, and observe the moving object by moving their sight to the moving direction of the moving object on the previous frame image. Furthermore, the eyes perform sampling of the image at intervals shorter than an inter-frame spacing of the moving image. As a result, the eyes visually recognize an image between two successive frames to compensate the spacing, thereby observing the blur phenomenon.
The problem can be solved by setting a shorter inter-frame spacing for displaying. This can also improve unnatural motion in a moving image with a few display frames. One of conceivable concrete approaches is to create an interpolation image by using motion compensation, which is used for an MPEG2, to interpolate between successive frames.
The motion compensation uses a motion vector detected by block matching. According to general block matching, an existing frame is divided into a plurality of blocks, and then each of the divided blocks is examined to search another frame for a similar area. Consequently, a motion vector between the divided block and the found similar area is obtained.
However, if an interpolation frame is created by using the motion vector obtained based on the existing frame, overlap or gap between blocks can be created on the interpolation frame, so that it is difficult to create a clean interpolation image.
To solve such problem, for example, Japanese Patent No. 2528103 and JP-A 2004-104656 (KOKAI) disclose a method for preventing creation of overlap or gap between blocks on an interpolation frame. According to the method, instead of the existing frame, the interpolation frame to be created is divided into a plurality of blocks, and then frames before and after the interpolation frame are searched.